[PATCH 4/8] arm64: add local_daif_inherit()

[James Morse <james.morse@arm.com>]

From: Mark Rutland <mark.rutland@arm.com>

Some synchronous exceptions can be taken from a number of contexts,
e.g. where IRQs may or may not be masked. In the entry assembly for
these exceptions, we use the inherit_daif assembly macro to ensure
that we only mask those exceptions which were masked when the exception
was taken.

So that we can do the same from C code, this patch adds a new
local_daif_inherit() function, following the existing local_daif_*()
naming scheme.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
[moved away from local_daif_restore()]
Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/arm64/include/asm/daifflags.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h
index 063c964af705..9207cd5aa39e 100644
--- a/arch/arm64/include/asm/daifflags.h
+++ b/arch/arm64/include/asm/daifflags.h
@@ -9,6 +9,7 @@
 
 #include <asm/arch_gicv3.h>
 #include <asm/cpufeature.h>
+#include <asm/ptrace.h>
 
 #define DAIF_PROCCTX		0
 #define DAIF_PROCCTX_NOIRQ	PSR_I_BIT
@@ -109,4 +110,19 @@ static inline void local_daif_restore(unsigned long flags)
 		trace_hardirqs_off();
 }
 
+/*
+ * Called by synchronous exception handlers to restore the DAIF bits that were
+ * modified by taking an exception.
+ */
+static inline void local_daif_inherit(struct pt_regs *regs)
+{
+	unsigned long flags = regs->pstate & DAIF_MASK;
+
+	/*
+	 * We can't use local_daif_restore(regs->pstate) here as
+	 * system_has_prio_mask_debugging() won't restore the I bit if it can
+	 * use the pmr instead.
+	 */
+	write_sysreg(flags, daif);
+}
 #endif
-- 
2.20.1


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